Thermoelectric devices convert temperature gradients into electricity and vice versa. Solid state thermal engine technology is based on thermionics. Thermionics originated nearly a century ago with a basic vacuum tube, a device that consists of two parallel conductive plates (a high temperature cathode and a low temperature anode) separated by a vacuum gap. During operation, electrons boil off the cathode, traverse the gap and then are absorbed into the colder anode, resulting in a net current between the anode and the cathode.
A conventional figure of merit for thermoelectric devices is the ZT factor, which takes into account the thermal power, electrical conductivity, thermal conductivity and temperature of the device. For many years, the ZT factor of traditional thermoelectric devices has been on the order of 1. Recent advances by the Research Triangle Institute have improved the ZT factor of certain devices up to approximately 2 to 2.5, as disclosed, for example, in U.S. Pat. No. 6,722,140 issued to Venkatasubramanian. Although desirable improvements in the ZT factor of thermoelectric devices have been achieved, in order to make thermoelectric devices more competitive with other types of power generation and cooling systems, further improvement may be needed.